1. Field of the Invention
The present invention relates generally to a method for controlling a SAR (Specific Absorption Rate) in a mobile communication terminal, and more particularly to an apparatus and method for controlling a SAR by controlling a transmission power of a mobile communication terminal.
2. Description of the Related Art
Recently, there has been an increasing controversy on the subject of whether electromagnetic waves emitted from electronic appliances are harmful to the human body. Particularly, it is well known that communication equipments directly brought into contact with the human body, for example, a mobile terminal such as a cellular phone and a PCS phone having a high SAR. Consequently, a variety of standards for protecting the human body from being exposed to harmful electromagnetic waves such as EMI (ElectroMagnetic Interference) have been recommended by national administrative organs and international organizations on the assumption that the EMI is harmful to the human body, and have been adapted as policy or recommendations in many countries. The United States has prohibited the sale of electronic appliances having a SAR of more than 1.6 W/Kg on the human head since 1997, and the MIC (Ministry of Information and Communication) in Korea has prescribed a SAR of 1.6 W/Kg as a standard for protecting the human body from EMI.
SAR, which indicates the amount of electromagnetic energy absorbed by the human body, is defined as absorption energy per mass (i.e., W/Kg) for a given time, and is expressed as follows:
                    SAR        =                              σ            ⁢                                                  ⁢                          E              i              2                                ρ                                    [                  Eq          .                                          ⁢          1                ]            where σ is electric conductivity of a human body, ρ is a density, and Ei is the magnitude of electric field. The SAR in human tissue is proportional to a square of electric field intensity, and is determined in light of parameters of an incident electromagnetic field, for example, frequency, intensity, direction, source, a relative position of a target subject, dielectric properties of human tissues exposed to EMI, influence of the ground, and EMI exposure environments.
A variety of conventional methods for reducing the influence of EMI on the human head have been proposed, for example, a method for attaching an EMI shield case to a mobile terminal, or a method for arranging an antenna far away from the human head. However, these conventional methods cannot completely remove EMI emitted from a mobile terminal even though they drop a SAR down to a prescribed standard, resulting in some fear for the user of the mobile terminal. Particularly, the conventional methods have disadvantages in that a transmission power may gradually increase in a weak electric field area, and thereby users may be exposed to a maximal EMI within an allowable reference range.